a1 Photo Tips

A picture taken in red light will look red - won’t it? And the same goes for pictures taken in other types of colored light. What you may not notice is that ordinary daylight can have very different qualities, and give very different results, depending on the time of day and other factors.

When the sun is close to the horizon, most of the blue rays are filtered out in the atmosphere and the light becomes reddish. And conversely, at noontime when the sun is as high up in the sky as it gets, the light is rather more blueish. This is especially true in the tropics - as in the image here above. At high altitudes, the light also has a very blue character since it has a shorter passage thru the atmosphere.

On an overcast day the cloud cover blocks much of the red wavelengths and for this reason the light that reaches the earth is rather cool.

Our human eyes adjust to these varying qualities of light, and unless they are quite extreme we don’t notice them much. The camera, however, faithfully records them as they are. Therefore we may be disappointed when we see how our pictures come out, with color casts we don’t like - unless we learn to understand how to deal with these effects.

You may be familiar with the term “color temperature”. Very cool blueish light is referred to as having a high color temperature, while reddish light as in the sunset picture here has - you guessed it - a low color temperature.

There is an international scale for measuring this, called the Kelvin scale. Unless you are seriously into Physics, you don’t need to know much about it, just take a look at the illustration here below to get a general idea.

A digital camera will be equipped with controls intended to compensate for those differences in color temperature of the light in different situations. For instance, my old Canon digicam has such settings as “Sunny” and “Cloudy”, plus a few more including - of course - “Auto”.

It is tempting to just set the camera on “Auto” and then forget about the whole issue. The problem is, as usual, that when you let the camera “think” for you, you also give up creative control over your pictures.

Naturally, how much creative leeway you have depends on what kind of camera you own. Like with my old Canon, I get to choose between a few standard types of lightning - or else set my own white balance. The latter means you point the digicam on a piece of white, or neutral grey, material; and set the camera to use that surface as a starting point for correct color balance in that particular situation.

With more advanced digicams, you could also have the option to set a number on the Kelvin scale directly. This opens the way for very precise and convenient control over the color rendering of every picture you take - provided you have the basic understanding shown in the illustration here.

Suppose for instance you take a picture on a cloudy day, when the colors are a bit on the cool side. You prefer to add just a bit of a warm “sunny” feeling to that picture. What to do? You set the Kelvin scale to a somewhat high number. By doing so, you tell the camera that the light is VERY blueish, and that this needs to be compensated for - by adding more red.

Or you are snapping a picture indoors in available light from incandescent light bulbs. You can then decide just how much of that “feeling” you want to have in the picture. Do you want to compensate fully for the reddish character of the incandescent light - or do you prefer to immerse the scene in a cozy reddish glow? In the latter case, you set the Kelvin scale to a higher number than the actual color temperature of the tungsten light sources, to get more red.

The Kelvin scale generally sees a color temperature of about 5500 K as “neutral white”, as shown above. Lower numbers mean an excess of red wavelenghts, and higher numbers mean an excess on the blue side.

Another situation where you may want to use a manual setting of the white balance is for very monochrome scenes. For instance, a picture of a person dressed in white and standing in front of a white wall. In this case the camera may have a hard time deciding what color balance setting to use, and needs your help.

Photo credits: bungalows by muha…; sunset by jurvetson.

Lately, I have been talking about the Exposure Triangle, and how you need to understand what it is all about to take creative control over your picture making.

In this post I figured I’d demonstrate one of the points of that imaginary triangle - the ISO setting.

Remember what the three points were?

Aperture - size of the light opening into the camera

Shutter Speed - how long time the shutter stays open

ISO Setting - sensitivity setting of the light-recording camera sensor

You may recall that I have told you the image quality gets impaired if you crank up the ISO-setting. OK, now I am going to show it to you, according to the old adage, “One picture is worth 1000 words.”

See the pictures above? Both are shot at the same aperture, but with different ISO-settings. For the one on the left I set my old Canon Powershot digicam at 50 ISO, and right after snapping that picture I changed to 400 ISO and snapped the picture to the right.

Well, in fact both of these are enlarged details of the original pictures; here below you can see what the original pictures looked like (I show the 50 ISO one here, the other looks just about the same).

The enlarged details show very clearly how the image quality gets degraded at high ISO-settings (400 ISO was the highest I could get with my camera, more advanced digicams allow for much higher ISO numbers). The difference is especially evident on perfectly smooth and uniform surfaces, like on cars.

Note how the surface looks quite grainy at 400 ISO.

– Hmmm, I wonder where they use such funny license plates on cars…?

The ISO scale is set so that each doubling of the numbers equals doubling the sensitivity; like ISO 400 is twice as sensitive a setting as ISO 200, which is twice as sensitive as ISO 100 - and so on. In other words, by sacrificing some of the image clarity I have made the camera sensor EIGHT TIMES more sensitive to light!

In low-light situations, this could mean the difference between getting a useable picture or not, like being able to shoot at 1/40 of a second rather than 1/5 - in the latter case it would be very difficult to avoid blur due to camera movement.

You may wonder how this image noise happens? Well, you probably know that a digital image is composed of an array of tiny squares called “pixels“. Each pixel can have its own color, thus forming a mosaic that builds up the total picture. Now imagine there is a tiny goblin sitting at each pixel, with the duty of trying to figure out the nature of the brief light pulse that arrives at that pixel when the picture is snapped.

At low ISO settings the goblin doesn’t need to make up its mind until there is enough light to make a good decision. But if you crank up the ISO-setting, each goblin is forced to decide based on very scanty data - more or less make an educated guess. And therefore the final image will be a bit of a guesswork.

Even if you don’t believe in goblins I’m sure you can follow my reasoning. So what have we learned today? Something like this maybe:

If all else fails, we can crank up the ISO-setting of a digital camera to get a picture where it otherwise wouldn’t have been possible.

In other words: avoid upping the ISO number unless it is really needed - or you don’t really care about the image quality. Note: you can set the ISO value on automatic on probably just about any digicam. If you do, make sure you know what is going on to avoid surprises. The camera may have a low opinion of your ability to hold it steady at slow shutter speeds.

Update: I should mention that advanced users may be interested in testing post-processing software which reduces such image noise as you get at high ISO-settings. Since I haven’t tested these myself I don’t know how good they are at improving the quality of such images, but I’ve seen that some swear by them.

In previous posts I have been talking about how to take control over your digital camera, rather than letting the camera control YOU.

This knob here is where you exert that control! Note that it isn’t set at the green “AUTO” mode - which is the mode for newbies.

Most of those other modes which are marked by symbols are also for newbies. They are meant to simplify things by allowing you to set an exposure mode optimized for some common type of subject matter. Like for instance: the head setting for portraits and so on.

In the picture here, the camera (which is my old Canon Powershot G2) is set at Aperture Priority mode. What that means is: the camera allows YOU to choose the aperture you like - then the camera tries to set the shutter speed to a value which balances that choice to make a correct exposure. I may also choose to include the ISO-setting as another variable which I allow the camera to play with, to get the exposure right. If so, I set the ISO to “Auto” (which is done in a menu not shown here).

Aperture Priority means precisely that - I am about to make a shot in a situation where the aperture setting is the most important one - the one I particularly want to control for getting the result I want.

In a previous post, Using Aperture For Creative Control, I gave you a few examples, like the image of a spiral staircase shot from below. In that picture, it was important to get everything in sharp focus for best effect. And how do you do that? Yes, by using as small an aperture as possible. (Remember: smaller apertures have larger numbers - like, f=2 is a large aperture, ie. a large opening; while f=16 is a small one.)

The smaller the aperture, the larger is the depth of field you get - remember?

Conversely, in some situations you prefer to have a sharp focus on a special subject of interest only, and make some other stuff in the background be blurred - thereby less distracting. Then you want a large aperture. If you set your digicam in Aperture Priority mode, you set yourself in control over these things. You concentrate on what’s important and let the camera do the rest.

OK, over to the next important setting on that camera knob: Shutter Speed Priority. (Marked “Tv“; T as in Time.) Here, you want total control over the shutter speed, ie. how long time the shutter stays open. Typically, this is important to control in situations where you are dealing with a moving subject - I usually take the example of a speeding car (or speeding fish), as in my previous article, Using Shutter Speed to Get Image Control.

By setting the camera to Shutter Priority, you make that your priority for creative control in a particular situation. - In the picture of a speeding police vehicle here, the photographer has used a moderate shutter speed like maybe 1/125 of a second while panning with the subject - thereby getting the background blurred (motion blur) and creating a feeling of movement.

Fast-moving subjects may require very fast shutter speeds, ie. short exposure times, to be rendered as sharp. To get enough light into the camera sensor in that short time, the camera will choose a larger aperture. How large an aperture you can get depends on the lens. A “fast” lens is made of large discs of glass to achieve a large maximum aperture, thereby allowing you to use a shorter exposure time - and this is why it’s called “fast”.

Summing up:

Use Aperture Priority when the aperture setting is the most important for you - that is, when you want to control the depth of field; either by extending it or shortening it.

Use Shutter Priority in those situations where you need to control exactly what shutter speed the camera uses - like to “freeze” the motion of fast-moving subjects.

And, yes, there is another setting you can use, too: “M” as in MANUAL! Then you set both shutter speed and aperture to whatever you please. Back in the old days before automation became the order of the day, this was how you made pictures. You measured the light, with a separate hand-held exposure meter, and then decided on a combo of shutter and aperture settings which seemed to fit the situation, before actually making the exposure. Well, you get the idea…

Photo credits: police vehicle by extranoise.